1. Field of The Invention
The invention relates generally to a system and method for electronically transmitting relatively short segments of full-motion video material from one geographic location to another.
2. Description of Prior Art
Various means of delivering full-motion video material from one location to another are in widespread use. Current methods include the physical delivery of a cassette, analog transmission via dedicated high-bandwidth coaxial cable, digital transmission via high-bandwidth switched fiber channels, transmission via satellite and transmission via radio. Each of these methods has its attendant limitations. Physical delivery of a cassette involves significant time and requires shipping arrangements to be made. High-bandwidth coaxial cable for analog transmission is not switchable or expandable, limiting service to fixed locations, whereas high bandwidth switched fiber channels are expensive and not widely available. Transmission via satellite is expensive and limited to fixed locations. Furthermore, considerable inconvenience is involved in scheduling delivery of the video material to the origination end, and picking up the video material on the receiving end and delivering it to the recipient. In the case of transmission via radio, a limited number of channels are available within the FCC-allocated spectrum, most of which are no wider bandwidth then is offered by the telephone network. Interconnectivity is also limited.
Video material is typically compressed prior to transmission. Current video compression approaches fall into two categories: "real-time" for video conferencing and editing uses, and "very non-real time" for media authoring uses. "Real time" compression and decompression is demanded by video conferencing systems where the total turnaround delay from user number one to user number two and back is critical. This requirement precludes the use of any off-line non-real-time compression methods. "Real time" compression and decompression is also used in all practical editing systems, because (1) of the need to play back at full frame rate randomly selected video segments, and (2) it permits the use of relatively low-cost video tape players which can only record and play back at full frame rate; hence video material must be outputed and digitized at this rate. The same argument is true for decompression and transfer to tape. Examples of this type of video compression are found in U.S. Pat. Nos. 4,843,466, 4,953,196, and 5,062,136.
"Very non-real time" compression refers to the use of a large powerful computer, located in a special facility, where video material is shipped for overnight compression. This is used in the media authoring, or publications market. An example of this type of video compression is found in U.S. Pat. 5,130,792.
Video compression methods may be further categorized in relation to compressed file format. There are two broad categories: "Intraframe" and "Inter-frame" methods, realizing that interframe formats almost always include intraframe elements. "Intraframe" compression preserves the individual frames after compression. This format is the most practical for editing applications where random access to individual frames is critical.
"Inter-frame" compression replaces selected frames with information which represents changes from past and/or future reference frames. Regenerating such a frame on a random access basis, along with the audio segment that goes with it is not easy. Therefore, this method is generally not used for digital editing systems.
Heretofore, there has not been a convenient, inexpensive, readily-available method of delivering relatively short segments of full motion video material from one location to another by electronic means. The present invention addresses this need.